Holographic Optical Information Recording/Reproducing Device and Holographic Optical Information Recording/Reproducing Method
a technology of optical information and recording/recording device, which is applied in the direction of hologram nature/properties, instruments, optical beam sources, etc., can solve the problems of difficult control of aberration, difficulty in exchanging discs, and the approach to high density recording by the shorter wavelength of the light source and the larger numerical aperture of the lens, so as to improve the quality of the reproduced signal and achieve fast transfer rate
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first embodiment
[0045]FIG. 1 is a schematic construction diagram showing a holographic optical information recording / reproducing device according to a first embodiment of the present invention. A laser light source 1 generates a laser beam having a wavelength of 532.1 nm for generating secondary higher harmonics of a YAG solid laser excited by a semiconductor laser. The light beam from the laser light source 1 has the diameter thereof expanded by a beam expander 7 after being reflected by a mirror 13. The expanded beam is incident on a half wavelength plate 9 and split into a signal light 25 and a reference light 22 by a beam splitter (polarizing beam splitter) 8. The light incident on the half wavelength plate 9 is a linearly polarized light and has, for example, a polarization component in a direction perpendicular to the plane of FIG. 1. By adjusting an angle of rotation of the half wavelength plate 9, a ratio of the polarization component perpendicular to the plane of FIG. 1 of the light incide...
second embodiment
[0072]FIG. 7 is a schematic diagram of a holographic optical information recording / reproducing device according a second embodiment of the present invention. A characteristic feature of the holographic optical information recording / reproducing device of FIG. 7 is that a polarization controlling device for controlling the power distribution ratio of a signal light and a reference light includes an EO modulator 91. The EO modulator 91 has a feature of being operable at high speed. Another characteristic feature of the holographic optical information recording / reproducing device is that one hologram is reproduced immediately after this hologram is recorded. The procedure of recording the hologram is as follows.
[0073]Upon recording a hologram, a reference light 22 and a signal light 25 are simultaneously irradiated to a holographic disc 5. At this time, a two-dimensional light receiving element array 6 is irradiated with the signal light 25 having transmitted through a spatial light mod...
third embodiment
[0091]If being left unexposed, a holographic material might experience problems that a reaction, different from a chemical reaction undergone during actual exposure, due to ambient environmental temperature, whereby the material is blackened to increase scattering and the like. In order to prevent this, it is useful to irradiate unexposed parts of the material with light to consume the unreacted material when no more information is written after the recording, i.e. the disc is closed. This is called a fixing process.
[0092]In the first embodiment, the refractive index differences are fixed by polymerizing all the remaining monomers when the entire recording is completed, and the holographic disc 5 can be irradiated with the light with a power density larger than the one used during the recording at the time of fixing the holograms. For example, during the fixing process, the monomers in the recording material are already polymerized by being consumed by the holographic recording and ...
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